A phosphor serves as a medium, which converts energy of an excitation source into energy of visible light. Thus, the phosphor is a necessary component for realizing an image on various display devices, and simultaneously, the phosphor is a main element directly related to efficiency of display products.
Three is a light emitting device using a blue light emitting diode, which is one of light emitting devices that emit white light. The light emitting device using the blue light emitting diode uses blue light as the excitation source and coats a yellow phosphor emitting yellow light onto a light emitting diode emitting the blue light. Thus, the blue light emitted from the blue light emitting diode and the yellow light emitted from the yellow phosphor are mixed with each other to realize the white light.
That is, the white light emitting device obtains the while light through a method in which the phosphor is coated on the blue light emitting diode to mix the blue light emitted from the blue light emitting diode with secondary light emitted from the phosphor, for example, a YAG:Ce phosphor emitting the yellow light is coated on the blue light diode to emit the white light.
However, according to the foregoing method, there are limitations that quantum deficits generated by using the secondary light and the reduction of optical efficiency due to re-radiation efficiency may occur, and it is difficult to realize superior color rendering. Thus, according to a related art white light emitting device, since a blue light emitting diode and a yellow phosphor are combined with each other, green and red color components are insufficient to display unnatural colors. As a result, the related art white light emitting diode has been used in limited fields such as screens of portable terminals, notebooks, personal computers (PCs), etc. Nevertheless, the related art white light emitting diode is being widely used because of easy driving operation a significantly low price.
Generally, it is widely known that silicates, phosphates, aluminates, or sulfides are used as phosphors for a mother material, and transition metals or rear earth metals are used as phosphors for luminescent center.
A phosphor, which is excited by an excitation source having high energy such as ultraviolet or blue light to emit visible light has been mainly developed in a white light emitting device field. However, when a related art phosphor is exposed to an excitation source, there is a limitation that luminance is reduced. In recent, researches with respect to a phosphor having a small luminance reduction, e.g., a host crystal of a silicon nitride-related ceramic are being progressed. As a result, a material, which has a stable crystal structure and shifts excitation light or emission light into a long wavelength, i.e., nitride or oxide nitride phosphor in the spotlight as the phosphor for the white light emitting device.
Particularly, an α-SiAlON:Eu yellow phosphor having photoluminescence emission superior than that of a YAG phosphor has been developed in 2002. Also, a CaAlSiN3:Eu red phosphor that is pure nitride has been developed in August, 2004, and a β-SiAlON:Eu green phosphor has been developed in March, 2005. When these phosphors are combined with the blue light emitting diode, colors having good color purity may be emitted. Particularly, since the light emitting diode has superior durability and small temperature variation, life cycle and reliability of a light source of the light emitting diode may be improved.
According to a novel light emitting device that is developed in recent, the blue light emitting diode, the α-SiAlON:Eu green phosphor, and the CaAlSiN3:Eu red phosphor may be improved and combined to convert light having a wavelength of about 460 nm and emitted through the blue light emitting diode into light having a wavelength of about 540 nm to about 570 nm and emitted through the green or yellow phosphors and light having a wavelength of about 650 nm and emitted through the red phosphor, thereby emitting three primary color light.